(1) Field of the Invention
The present invention relates to novel and highly advantageous N-carboxy alkyl amino alkane polyphosphonic acids and their alkali metal salts and more particularly to such polyphosphonic acids which have more than two carbon atoms in their carboxy alkyl group, to a process of producing such compounds, and to compositions for and a method of using the same.
(2) Description of the Prior Art
In German Pat. No. 23 18 416 there are described N-carboxy methyl amino alkane or aryl alkane diphosphonic acids. Such acids are produced by reacting amino alkane or aryl alkane diphosphonic acids in an alkaline medium with formaldehyde and an alkali metal cyanide at a temperature between about 70.degree. C. and about 150.degree. C. By cyano alkylation there are obtained the corresponding cyano methyl aminoalkane or aryl alkane diphosphonic acids.
Subsequently the nitrile group of the resulting compounds is saponified to the carboxyl group.
The phosphonic acids described in said patent are characterized by a high water solubility, by a satisfactory complexing and sequestering power with respect to polyvalent metal ions and when used even in sub-stoichiometric amounts, by an especially high stabilizing power with respect to the hardness-forming compounds present in water.
The disadvantages of the process of producing such compounds according to said German Patent No. 23 18 416 are that only carboxy methyl amino alkane or aryl alkane phosphonic acids can be produced in a satisfactory manner and that working with alkali metal cyanides requires extensive precautionary measures in carrying out this process. Higher molecular carboxy alkyl compounds could not be prepared in a satisfactory yield by using higher aldehydes in place of formaldehyde.